(1) Field of the Invention
The present invention generally relates to a method of determining driving signals for an organic electroluminescence device, and more particularly, to a full-color Active Matrix organic electroluminescence device, which comprises white organic light emitting diode (OLED).
(2) Description of the Prior Art
Organic electroluminescence device has the advantages of high luminance, high reactive speed, relatively thin and small size, full color and absence of backlight source. Therefore, it has been considered as one of the primary competitors of the Liquid Crystal Display (LCD) in the display market. In fact, the organic electroluminescence device has been applied to portable IT (Information Technology) product such as mobile phone, Personal Digital Assistant (PDA), digital camera or et cetera.
Technologies about fabricating the organic electroluminescence device are promoted rapidly in response to the market's demands. To display full colors, the typical means is utilizing a red sub-pixel, blue sub-pixel and a green sub-pixel, usually a red OLED, a blue OLED and a green OLED respectively, to compose a pixel. In other words, the traditional method, which is very common in the display field, is utilizing three primary colors to compose other colors that demand. A plurality of the mentioned pixel is arranged as an array and is disposed on the display panel so as to present full-color images. In the following paragraphs, “three-color organic electroluminescence device” indicates this kind of prior art.
Base on the consideration of electricity consumption, another technique was therefore provided. At least one white OLED is used to have a white sub-pixel, a red sub-pixel, a blue sub-pixel and a green sub-pixel so as to compose a single pixel having four primary colors. In the following paragraphs, “four-color organic electroluminescence device” indicates this art.
The electricity consumption of the four-color organic electroluminescence device only reaches half, or lower, of the three-color organic electroluminescence device. Its functions are described below correlating with FIG. 1A and FIG. 1B. FIG. 1A is a CIE chromaticity diagram of a prior three-color organic electroluminescence device. FIG. 1B is a CIE chromaticity diagram of a prior four-color organic electroluminescence device.
Please refer to FIG. 1A. While having a pixel display a predetermined color C1, in a three-color organic electroluminescence device, the red sub-pixel generates luminance R1; the blue sub-pixel generates luminance B1; and the green sub-pixel generates luminance G1, so as to compose the predetermined color C1.
Please refer to FIG. 1B. While having a pixel display a predetermined color C1, in a four-color organic electroluminescence device, the white sub-pixel generates luminance W1; the red sub-pixel generates luminance R2; the blue sub-pixel generates luminance B2; and the green sub-pixel generates luminance G2. Because the four-color organic electroluminescence device comprises the white OLED generating the luminance W1; and also because the white color is composed of red, green and blue. Luminance R2, luminance B2 and luminance G2 are respectively lower than luminance R1, luminance B1 and luminance G1 shown in FIG. 1A. In other words, adding the white sub-pixel is able to reduce the electricity consumption of the other three sub-pixels. Therefore, the general advantage of the four-color organic electroluminescence device over the three-color organic electroluminescence device is power saving.
However, there are still several problems to overcome while actually putting the four-color organic electroluminescence device on product lines. For example, the emission spectrum of the white OLED, under different operating voltages, shows relatively large shifting than OLEDs of other colors. Pleas refer to FIG. 2. It shows individual emission spectraspectra of white OLED under operating voltages of 5V, 6V, 7V and 8V, respectively. Obviously, the emission spectraspectra shift at a noteworthy level. As a result, it shows “different white” under different voltages, and the color shifting problem becomes the major drawback of four-color organic electroluminescence device.
The white OLED is relatively unstable as the red OLED, blue OLED and the green OLED. Under different operating voltages, the white OLED shows different white. Therefore, the proportion of red, green and blue from the white sub-pixel changes under different voltages. This may result in a drawback of color distortion. For this reason, to provide a four-color organic electroluminescence device, which has the remarkable power saving property, without the mentioned color distortion problem is the primary aim of the present invention.